Semiconductor nanocrystal particles, production methods thereof, and devices including the same

ABSTRACT

A method of producing a quantum dot comprising zinc selenide, the method comprising: providing an organic ligand mixture comprising a carboxylic acid compound, a primary amine compound, a secondary amide compound represented by Chemical Formula 1, and a first organic solvent:RCONHR  Chemical Formula 1wherein each R is as defined herein;heating the organic ligand mixture in an inert atmosphere at a first temperature to obtain a heated organic ligand mixture;adding a zinc precursor, a selenium precursor, and optionally a tellurium precursor to the heated organic ligand mixture to obtain a reaction mixture, wherein the zinc precursor does not comprise oxygen; andheating the reaction mixture at a first reaction temperature to synthesize a first semiconductor nanocrystal particle.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/170,493, filed Oct. 19, 2018, which claims priority to and thebenefit of Korean Patent Application No. 10-2017-0139603 filed in theKorean Intellectual Property Office on Oct. 25, 2017, and all thebenefits accruing therefrom under 35 U.S.C. § 119, the entire contentsof which are incorporated herein by reference.

BACKGROUND 1. Field

A semiconductor nanocrystal particle, a production method thereof, and adevice including the same are disclosed.

2. Description of the Related Art

Unlike bulk materials, intrinsic physical characteristics (e.g., energybandgaps and melting points) of nanoparticles may be controlled bychanging the nanoparticle sizes. For example, a semiconductornanocrystal particle (also known as a quantum dot) is a crystallinematerial having a particle size of several nanometers. The semiconductornanocrystal particle has a small particle size that provides a largesurface area per unit volume and exhibits a quantum confinement effect,and thus may have different properties than bulk materials having thesame composition. A quantum dot may absorb light from an excitationsource to be excited, and may emit energy corresponding to its energybandgap.

SUMMARY

An embodiment provides a cadmium-free semiconductor nanocrystal particlecapable of emitting light of a desired wavelength with an enhancedefficiency and a narrowed full width at half maximum (FWHM) and aproduction method thereof.

An embodiment provides an electronic device including the semiconductornanocrystal particle.

In an embodiment, a method of producing a quantum dot including zincselenide (ZnSe) is provided, the method including:

providing an organic ligand mixture including a carboxylic acidcompound, a primary amine compound, a secondary amide compoundrepresented by Chemical Formula 1, and a first organic solvent:RCONHR  Chemical Formula 1

wherein each R is the same or different and each independently is asubstituted or unsubstituted aliphatic hydrocarbon having a carbonnumber of greater than or equal to 5, a substituted or unsubstitutedalicyclic hydrocarbon having a carbon number of greater than or equal to3, or a substituted or unsubstituted aromatic hydrocarbon having acarbon number of greater than or equal to 6;

heating the organic ligand mixture in an inert atmosphere at a firsttemperature to obtain a heated organic ligand mixture;

adding a zinc precursor, a selenium precursor, and optionally atellurium precursor to the heated organic ligand mixture to obtain areaction mixture, wherein the zinc precursor does not include oxygen(e.g., a zinc-oxygen bond); and

heating the reaction mixture at a first reaction temperature tosynthesize a first semiconductor nanocrystal particle.

The carboxylic acid compound may include a compound represented byChemical Formula 2, and/or the primary amine compound may include acompound represented by Chemical Formula 3:R¹COOH  Chemical Formula 2R²NH₂  Chemical Formula 3

wherein R¹ and R² are the same or different and each independently is asubstituted or unsubstituted aliphatic hydrocarbon having a carbonnumber of greater than or equal to 5, a substituted or unsubstitutedalicyclic hydrocarbon having a carbon number of greater than or equal to3, a substituted or unsubstituted aromatic hydrocarbon having a carbonnumber of greater than or equal to 6, or a combination thereof;

The carboxylic acid compound may include pentanoic acid, hexanoic acid,heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoicacid, dodecanoic acid, tridecanoic acid, tetradecanoic acid,pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoicacid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, docosanoicacid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid,hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoicacid, triacontanoic acid, tetra-triacontanoic acid, pentatriacontanoicacid, hexatriacontanoic acid, alpha linolenic acid, eicosapentaenoicacid, docosahexaenoic acid, linolenic acid, gamma-linolenic acid,dihomo-gamma-linolenic acid, arachidonic acid, paullinic acid, oleicacid, elaidic acid, eicosenoic acid, erucic acid, nervonic acid, or acombination thereof.

The primary amine compound may include a pentylamine, hexylamine,heptylamine, octylamine, nonylamine, decylamine, undecylamine,dodecylamine, tridecylamine, pentadecylamine, hexadecylamine,heptadecylamine, ocatdecylamine, nonadecylamine, oleylamine, or acombination thereof.

The secondary amide compound may include two different aliphatichydrocarbon groups each independently having a carbon number of 10 to40.

The providing of the organic ligand mixture may include heating thecarboxylic acid compound and the primary amine compound in the organicsolvent at a temperature of greater than or equal to about 200° C. forabout 10 minutes or longer.

An amount of the primary amine compound (e.g., in the organic ligandmixture) may be greater than or equal to about 0.5 moles with respect to1 mole of the carboxylic acid compound.

An amount of the primary amine compound (e.g., in the organic ligandmixture) may be less than or equal to about 3 moles with respect to 1mole of the carboxylic acid compound.

An amount of the primary amine compound (e.g., in the organic ligandmixture) may be less than or equal to about 2 moles with respect to 1mole of the carboxylic acid compound.

An amount of the primary amine compound (e.g., in the organic ligandmixture) may be less than or equal to about 1 moles with respect to 1mole of the carboxylic acid compound.

An amount of the carboxylic acid compound in the reaction mixture may begreater than or equal to about 0.1 moles and less than or equal to about10 moles based on 1 mole of the zinc precursor.

An amount of the primary amine compound (e.g., in the reaction mixture)may be greater than or equal to about 0.1 moles and less than or equalto about 10 moles based on 1 mole of the zinc precursor.

An amount of the secondary amide compound (e.g., in the reactionmixture) may be greater than or equal to about 0.1 moles and less thanor equal to about 10 moles based on 1 mole of the zinc precursor.

The first organic solvent may include a secondary amine having at leastone C6 to C40 aliphatic hydrocarbon (e.g., alkyl or alkenyl) group(e.g., a C12 to C40 secondary amine compound), a tertiary amine havingat least one C6 to C40 aliphatic hydrocarbon (e.g., alkyl or alkenyl)group (e.g., a C18 to C60 tertiary amine compound), anitrogen-containing heterocyclic compound, a C6 to C50 aliphatichydrocarbon, a C6 to C60 aromatic hydrocarbon, a phosphine compoundhaving at least one C6 to C22 alkyl group (e.g., a C6 to C60 phosphinecompound), a phosphine oxide having at least one C6 to C22 aliphatichydrocarbon (e.g., alkyl or alkenyl) group (e.g., a C6 to C60 phosphineoxide), a C12 to C22 aromatic ether, or a combination thereof.

The first temperature may be greater than or equal to about 240° C. andless than or equal to about the first reaction temperature.

The zinc precursor may include a zinc powder, an alkylated zinccompound, a zinc halide, a zinc cyanide, or a combination thereof.

The selenium precursor may include selenium-trioctylphosphine (Se-TOP),selenium-tributylphosphine (Se-TBP), selenium-triphenylphosphine(Se-TPP), selenium-diphenylphosphine (Se-DPP), or a combination thereof.

The tellurium precursor may include tellurium-trioctylphosphine(Te-TOP), tellurium-tributylphosphine (Te-TBP),tellurium-triphenylphosphine (Te-TPP), tellurium-diphenylphosphine(Te-DPP), or a combination thereof.

The first reaction temperature may be greater than or equal to about270° C.

The first reaction temperature may be less than or equal to about 350°C.

The first semiconductor nanocrystal particle may includeZnSe_(1−x)Te_(x) (wherein, x is greater than about 0 and less than orequal to about 0.2).

A size of the first semiconductor nanocrystal particle may be greaterthan or equal to about 2 nanometers.

A size of the first semiconductor nanocrystal particle may be less thanor equal to about 5 nanometers.

The method may further include providing a first shell precursorsolution including a metal-containing first shell precursor, an organicligand, and a second organic solvent;

providing a second shell precursor including a non-metal element; and

heating the first shell precursor solution at a second reactiontemperature and adding the first semiconductor nanocrystal particle andthe second shell precursor thereto to form a shell including a secondsemiconductor nanocrystal on the first semiconductor nanocrystalparticle.

The metal-containing first shell precursor may include zinc, and thesecond shell precursor may include selenium, sulfur, or a combinationthereof.

The organic ligand may include RCOOH, RNH₂, R₂NH, R₃N, RSH, RH₂PO,R₂HPO, R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR, RPO(OH)₂, RHPOOH, R₂POOH, or acombination thereof, wherein R is the same or different andindependently is a C1 to C40 substituted or unsubstituted aliphatichydrocarbon group, a C6 to C40 substituted or unsubstituted aromatichydrocarbon group, or a combination thereof.

The second organic solvent may include a primary amine having a C6 toC40 (aliphatic) hydrocarbon (e.g., alkyl or alkenyl) group (e.g., a C6to C40 primary amine compound), a secondary amine having at least one C6to C40 (aliphatic) hydrocarbon (e.g., alkyl or alkenyl) group (e.g., aC6 to C40 secondary amine compound), a tertiary amine having at leastone C6 to C40 (aliphatic) hydrocarbon (e.g., alkyl or alkenyl) group(e.g., a C6 to C40 tertiary amine compound), a nitrogen-containingheterocyclic compound, a C6 to C50 aliphatic hydrocarbon, a C6 to C50aromatic hydrocarbon, a phosphine compound having at least one C6 to C22(aliphatic) hydrocarbon (e.g., alkyl or alkenyl) group (e.g., a C6 toC60 phosphine compound), a phosphine oxide compound having at least oneC6 to C22 (aliphatic) hydrocarbon (e.g., alkyl or alkenyl) group (e.g.,a C6 to C60 phosphine oxide compound), a C12 to C22 aromatic ether, or acombination thereof.

In another embodiment, a quantum dot includes a core including a firstsemiconductor nanocrystal material including zinc, tellurium, andselenium; and a shell disposed on at least a portion of the core andincluding a second semiconductor nanocrystal material different from thefirst semiconductor nanocrystal material,

wherein the quantum dot does not include cadmium,

wherein the quantum dot has a maximum photoluminescent emission peak ina wavelength range of greater than or equal to about 440 nanometers (nm)and less than or equal to about 540 nm, and

wherein the quantum dot has a quantum efficiency of greater than orequal to about 60%.

The first semiconductor nanocrystal material may includeZnSe_(1−x)Te_(x) (wherein, x is greater than about 0 and less than orequal to about 0.2).

The second semiconductor nanocrystal material may include ZnSeS.

The shell has a gradient composition varying in a radial direction fromthe core.

The quantum dot has a maximum photoluminescent emission peak having afull width at half maximum (FWHM) of less than or equal to about 40 nm.

The quantum dot may have a multi-pod shape.

The quantum dot may have quantum efficiency of greater than or equal toabout 70%.

The quantum dot may have quantum efficiency of greater than or equal toabout 80%.

The quantum dot may have a particle size of greater than or equal toabout 3 nm.

The semiconductor nanocrystal particle may have a particle size of lessthan or equal to about 30 nm.

The semiconductor nanocrystal particle may not include cadmium.

In an embodiment, an electronic device includes the aforementionedquantum dot.

The electronic device may be a display device, a light emitting diode(LED), a quantum dot light emitting diode (QLED), an organic lightemitting diode (OLED), a sensor, an image sensor, or a solar cell.

A cadmium-free semiconductor nanocrystal particle capable of emittinglight of a desired wavelength (e.g., blue light) with an improvedefficiency and a narrowed FWHM may be provided. The semiconductornanocrystal particle may be applied to various display devices,biolabeling (biosensor, bioimaging), a photodetector, a solar cell, ahybrid composite, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic view illustrating a part of a process for forminga particle via using a ligand mixture in a production method of asemiconductor nanocrystal particle according to a non-limitingembodiment;

FIG. 2 is a schematic cross-sectional view of a quantum dot (QD) lightemitting diode (LED) device according to a non-limiting embodiment.

FIG. 3 is a schematic cross-sectional view of a QD LED device accordingto a non-limiting embodiment.

FIG. 4 is a schematic cross-sectional view of a QD LED device accordingto a non-limiting embodiment.

FIG. 5 is a graph of absorbance (arbitrary units, a.u.) versuswavenumber (inverse centimeters, cm⁻¹) and shows a result of Fouriertransform infrared spectroscopy (FT-IR) for an amide organic ligandcompound synthesized in Reference Example 1;

FIG. 6 is a graph of intensity (a.u.) versus chemical shift 8 (parts permillion, ppm) and shows Nuclear Magnetic Resonance (NMR) spectra of amixture prior to being heat-treated (top spectrum) and an amide organicligand compound synthesized via a thermal treatment in Reference Example1 (bottom spectrum);

FIG. 7 shows a transmission electron microscope (TEM) image of theZnTeSe cores produced in Example 1-1.

FIG. 8 shows a TEM image of the core-shell quantum dot produced inExample 1-2.

FIG. 9 is a graph of intensity (a.u.) versus wavelength (nanometers, nm)and shows ultraviolet-visible (UV-vis) absorption spectra of the coreparticles (solid line) and the core-shell quantum dots (dashed line)prepared in Example 1.

FIG. 10 is a graph of intensity (a.u.) versus wavelength (nm) and showsphotoluminescent emission spectra of the core particles (solid line) andthe core-shell quantum dots (dashed line) prepared in Example 1.

FIG. 11 shows a transmission electron microscope (TEM) image of theZnTeSe cores produced in Example 2-1.

FIG. 12 shows a transmission electron microscope (TEM) image of theZnTeSe cores produced in Comparative Example 1-1.

FIG. 13 shows a transmission electron microscope (TEM) image of theZnTeSe cores produced in Example 4-1.

FIG. 14 shows a TEM image of the core-shell quantum dot produced inExample 4-2.

DETAILED DESCRIPTION

Advantages and characteristics of this disclosure, and a method forachieving the same, will become evident referring to the followingexample embodiments together with the drawings attached hereto. However,the embodiments should not be construed as being limited to theembodiments set forth herein. Unless otherwise defined, all terms usedin the specification (including technical and scientific terms) may beused with meanings commonly understood by a person having ordinaryknowledge in the art. The terms defined in a generally-used dictionarymay not be interpreted ideally or exaggeratedly unless clearly defined.In addition, unless explicitly described to the contrary, the word“comprise” and variations such as “comprises” or “comprising”, will beunderstood to imply the inclusion of stated elements but not theexclusion of any other elements.

Further, the singular includes the plural unless mentioned otherwise.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification.

It will be understood that when an element such as a layer, film,region, or substrate is referred to as being “on” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, and/or sections, these elements,components, regions, layers, and/or sections should not be limited bythese terms. These terms are only used to distinguish one element,component, region, layer, or section from another element, component,region, layer, or section. Thus, “a first element,” “component,”“region,” “layer,” or “section” discussed below could be termed a secondelement, component, region, layer, or section without departing from theteachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” It will be further understood that the terms “comprises” and/or“comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±10%, or 5% of the stated value.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

As used herein, when a definition is not otherwise provided,“substituted” refers to a compound or a moiety wherein at least one ofthe hydrogen atoms thereof is replaced by a substituent, provided thatthe substituted atom's normal valence is not exceeded, wherein thesubstituent may be a C1 to C30 alkyl group, a C2 to C30 alkenyl group, aC2 to C30 alkynyl group, a C6 to C30 aryl group, a C7 to C30 alkylarylgroup, a C1 to C30 alkoxy group, a C1 to C30 heteroalkyl group, a C3 toC30 heteroalkylaryl group, a C3 to C30 cycloalkyl group, a C3 to C15cycloalkenyl group, a C6 to C30 cycloalkynyl group, a C2 to C30heterocycloalkyl group, a halogen (—F, —Cl, —Br, or —I), a hydroxy group(—OH), a nitro group (—NO₂), a cyano group (—CN), an amino group (—NRR′wherein R and R′ are independently hydrogen or a C1 to C6 alkyl group),an azido group (—N₃), an amidino group (—C(═NH)NH₂)), a hydrazino group(—NHNH₂), a hydrazono group (═N(NH₂)), an aldehyde group (—C(═O)H), acarbamoyl group (—C(O)NH₂), a thiol group (—SH), an ester group(—C(═O)OR, wherein R is a C1 to C6 alkyl group or a C6 to C12 arylgroup), a carboxyl group (—COOH) or a salt thereof (—C(═O)OM, wherein Mis an organic or inorganic cation), a sulfonic acid group (—SO₃H) or asalt thereof (—SO₃M, wherein M is an organic or inorganic cation), aphosphoric acid group (—PO₃H₂) or a salt thereof (—PO₃MH or —PO₃M₂,wherein M is an organic or inorganic cation), or a combination thereof.

As used herein, a “hydrocarbon group” refers to a group including carbonand hydrogen (e.g., an alkyl, alkenyl, alkynyl, or aryl group). Thehydrocarbon group may be a group having a monovalency or greater, forexample a monovalent, divalent, or tetravalent group, formed by removalof one or more hydrogen atoms from, for example, an aliphatic oraromatic hydrocarbon such as alkane, alkene, alkyne, or arene. In thehydrocarbon group, at least one methylene (—CH₂—) moiety may be replacedby an oxide moiety (—O—), a carbonyl moiety (—C═O—), an ester moiety(—COOR wherein R is an alkyl, alkenyl, alkynyl, or aryl group), an aminomoiety (—NH—), or a combination thereof. Alternatively, the hydrocarbongroup may consist of carbon and hydrogen.

As used herein, “aliphatic” refers to a saturated or unsaturated linearor branched hydrocarbon group having at least one carbon atoms (forexample, 5 to 40 carbon atoms, for example 6 to 24 carbon atoms). Analiphatic group may be an alkyl, alkenyl, or alkynyl group, for example.

As used herein, “alicyclic” refers to a cyclic hydrocarbon havingproperties of an aliphatic group. The alicyclic group may be a C5 to C40cycloalkyl group, a C5 to C40 cycloalkenyl group, or a C5 to C40cycloalkynyl group.

As used herein, “alkyl” refers to a linear or branched saturatedmonovalent hydrocarbon group (e.g., methyl, ethyl, hexyl, or the like).

As used herein, “alkenyl” refers to a linear or branched monovalenthydrocarbon group having one or more carbon-carbon double bond.

As used herein, “alkynyl” refers to a linear or branched monovalenthydrocarbon group having one or more carbon-carbon triple bond.

As used herein, “aryl” is an aromatic hydrocarbon and refers to a cyclicmoiety including carbon atoms in which at least one ring is aromatic,the moiety having the specified number of carbon atoms, specifically 6to 40 carbon atoms, more specifically 6 to 24 carbon atoms. More thanone ring may be present, and any additional rings may be independentlyaromatic, saturated or partially unsaturated, and may be fused, pendant,spirocyclic or a combination thereof. The term “aryl” may include aheteroaryl group including at least one heteroatom. Alternatively, inthe aryl group, all ring members may be carbon. Exemplary aromatichydrocarbon groups include phenyl, naphthyl, benzyl, or the like.

As used herein, “cycloalkyl” refers to a group that comprises one ormore saturated and/or partially saturated rings in which all ringmembers are carbon, such as cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl, cyclooctyl, adamantyl and partially saturatedvariants of the foregoing, such as cycloalkenyl groups (e.g.,cyclohexenyl) or cycloalkynyl groups. Cycloalkyl groups do not includean aromatic ring or a heterocyclic ring. When the numbers of carbonatoms is specified (e.g., C3 to C15 cycloalkyl), the number means thenumber of ring members present in the one or more rings.

As used herein, when a definition is not otherwise provided, the term“hetero” refers to inclusion of one or more (e.g., 1 to 3) heteroatomsthat can be N, O, S, Si, P, or a combination thereof.

As used herein, an “amine” group may have a general formula NRR, whereineach R is independently hydrogen, an alkyl group, or an aryl group, butis not limited thereto. “Primary amine” may be an amine having theformula RNH₂, wherein R is hydrogen, an alkyl group, or an aryl group,but is not limited thereto. “Secondary amine” may be an amine having theformula RR′NH, wherein R and R′ are each independently an alkyl group,an aryl group, or the like, but is not limited thereto. “Tertiary amine”may be an amine having the formula RR′R″N, wherein R, R′, and R″ areeach independently an alkyl group, an aryl group, or the like, but isnot limited thereto. “Amino” has the general formula —N(R)₂, whereineach R is independently hydrogen, a C1 to C6 alkyl, or a C6 to C12 aryl.

As used herein, “heterocyclic” refers to a cyclic group comprising atleast one ring member that is a heteroatom. If multiple rings arepresent, each ring is independently aromatic, saturated or partiallyunsaturated and multiple rings, if present, may be fused, pendant,spirocyclic or a combination thereof. Heterocycloalkyl groups compriseat least one non-aromatic ring that contains a heteroatom ring member.Heteroaryl groups comprise at least one aromatic ring that contains aheteroatom ring member. Non-aromatic and/or carbocyclic rings may alsobe present in a heteroaryl group, provided that at least one ring isboth aromatic and contains a ring member that is a heteroatom.

As used herein, “phosphine” has the general formula P(R)₃, wherein eachR is independently hydrogen, an aliphatic group (e.g., alkyl or alkenyl)group, or an aromatic group.

As used herein, “phosphine oxide” has the general formula PO(R)3,wherein each R is independently hydrogen, an aliphatic group (e.g.,alkyl or alkenyl) or an aromatic group.

As used herein, “Group” refers to a group of Periodic Table.

As used herein, the term “quantum yield” (QY) or the term “quantumefficiency (QE) is a value determined from a photoluminescence (PL)spectrum obtained by dispersing quantum dots in an appropriate solvent(e.g., toluene or hexane), and may be calculated with respect to thephotoluminescent peak of an organic solution of a reference dye (e.g.,an ethanol solution of an appropriate dye having an appropriateabsorption (optical density) at a predetermined wavelength). As usedherein, the term “quantum yield (QY)” and the term “quantum efficiency(QE)” may have substantially the same meaning and can be usedinterchangeably.

Semiconductor nanocrystal particles (hereinafter, also referred to as aquantum dot) may absorb light from an excitation source and may emitlight corresponding to an energy bandgap thereof. The energy bandgap ofthe quantum dot may be changed depending on a particle size and acomposition thereof. For example, as the particle size of the quantumdot increases, the quantum dot may have a narrower energy bandgap andmay show an increased light emitting wavelength. Semiconductornanocrystals have drawn attention as a light emitting material invarious fields such as a display device, an energy device, or a biolight emitting device.

Most of quantum dots having a satisfactory level of a photoluminescenceproperty for application include cadmium (Cd). The cadmium may raisesevere environmental and/or health issues and is a restricted elementdefined under Restriction of Hazardous Substances Directive (RoHS) in aplurality of countries. Accordingly, there remain needs for developmentof a cadmium-free quantum dot having improved photoluminescencecharacteristics. In order to be applied to a QLED display device, aquantum dot having a relatively narrow full width at half maximum (FWHM)and capable of emitting light of a desired wavelength (e.g., a pure blueat PL peak around 455 nm or a green light at PL peak around 530 nm) maybe desired. For example, a material capable of emitting light with anarrower FWHM and an enhanced efficiency may be required for a displaydevice having a relatively high color reproducibility under a nextgeneration color standard such as BT2020. Synthesis of a cadmium-freequantum dot having desirable photoluminescence properties and theaforementioned PL peak is not easy or has not been reported yet. Acore-shell structure may improve photoluminescence properties of quantumdots, but most of conventional core-shell quantum dots having desirableproperties include cadmium. Provided herein are cadmium-freesemiconductor nanocrystal particles having desirable photoluminescenceproperties.

An embodiment is a method of producing a semiconductor nanocrystalparticle including zinc selenide (ZnSe). As used herein, the term “zincselenide” (ZnSe) refers to a type of a metal chalcogenide including atleast zinc and selenium. The zinc selenide may further includeadditional elements such as tellurium. The method includes:

providing an organic ligand mixture including a carboxylic acidcompound, a primary amine compound, a secondary amide compoundrepresented by Chemical Formula 1, and an organic solvent:RCONHR  Chemical Formula 1

wherein each R is the same or different and each independently is asubstituted or unsubstituted aliphatic hydrocarbon having a carbonnumber of greater than or equal to 5 (e.g., greater than or equal to 6,for example, greater than or equal to 7, greater than or equal to 8,greater than or equal to 9, greater than or equal to 10, greater than orequal to 11, greater than or equal to 12, greater than or equal to 13,greater than or equal to 14, greater than or equal to 15, greater thanor equal to 16, greater than or equal to 17, greater than or equal to18, or greater than or equal to 19) and less than or equal to 40 (e.g.,less than or equal to 30, or less than or equal to 24), a substituted orunsubstituted alicyclic hydrocarbon having a carbon number of greaterthan or equal to 3 (e.g., greater than or equal to 6, for example,greater than or equal to 7, greater than or equal to 8, greater than orequal to 9, greater than or equal to 10, greater than or equal to 11,greater than or equal to 12, greater than or equal to 13, greater thanor equal to 14, greater than or equal to 15, greater than or equal to16, greater than or equal to 17, greater than or equal to 18, or greaterthan or equal to 19) and less than or equal to 40 (e.g., less than orequal to 30, or less than or equal to 24), or a substituted orunsubstituted aromatic hydrocarbon having a carbon number of greaterthan or equal to 6 (e.g., greater than or equal to 7, for example,greater than or equal to 8, greater than or equal to 9, greater than orequal to 10, greater than or equal to 11, greater than or equal to 12,greater than or equal to 13, greater than or equal to 14, greater thanor equal to 15, greater than or equal to 16, greater than or equal to17, greater than or equal to 18, or greater than or equal to 19) andless than or equal to 40 (e.g., less than or equal to 30, or less thanor equal to 24), or a combination thereof;

heating the organic ligand mixture in an inert atmosphere at a firsttemperature;

adding a zinc precursor, a selenium precursor, and optionally atellurium precursor to the heated organic ligand mixture to obtain areaction mixture, wherein the zinc precursor does not include oxygen;and

heating the reaction mixture at a first reaction temperature tosynthesize a first semiconductor nanocrystal particle (hereinafter, alsoreferred to as a core particle).

The zinc precursor may not include a zinc-oxygen bond.

The carboxylic acid compound may include a compound represented byChemical Formula 2, and the primary amine compound may include acompound represented by Chemical Formula 3:R¹COOH  Chemical Formula 2R²NH₂  Chemical Formula 3

wherein R¹ and R² are the same or different and are each independently asubstituted or unsubstituted aliphatic hydrocarbon (e.g., a straight orbranched alkyl, alkenyl, or alkynyl) having a carbon number of greaterthan or equal to 5 (e.g., greater than or equal to 6, for example,greater than or equal to 7, greater than or equal to 8, greater than orequal to 9, greater than or equal to 10, greater than or equal to 11,greater than or equal to 12, greater than or equal to 13, greater thanor equal to 14, greater than or equal to 15, greater than or equal to16, greater than or equal to 17, greater than or equal to 18, or greaterthan or equal to 19, or for example C5 to C40, or C6 to C24), asubstituted or unsubstituted alicyclic hydrocarbon (e.g., cyclohexyl,cyclodecyl, tricyclodecyl, norbonyl, or the like) having a carbon numberof greater than or equal to 3 (e.g., greater than or equal to 6, forexample, greater than or equal to 7, greater than or equal to 8, greaterthan or equal to 9, greater than or equal to 10, greater than or equalto 11, greater than or equal to 12, greater than or equal to 13, greaterthan or equal to 14, greater than or equal to 15, greater than or equalto 16, greater than or equal to 17, greater than or equal to 18, orgreater than or equal to 19, or for example C5 to C40, or C6 to C24), asubstituted or unsubstituted aromatic hydrocarbon (e.g., aryl such asphenyl, naphthyl, or benzyl, or the like) having a carbon number ofgreater than or equal to 6 (e.g., greater than or equal to 6, forexample, greater than or equal to 7, greater than or equal to 8, greaterthan or equal to 9, greater than or equal to 10, greater than or equalto 11, greater than or equal to 12, greater than or equal to 13, greaterthan or equal to 14, greater than or equal to 15, greater than or equalto 16, greater than or equal to 17, greater than or equal to 18, orgreater than or equal to 19, or for example C6 to C40, or C6 to C24), ora combination thereof;

The carboxylic acid compound may include pentanoic acid, hexanoic acid,heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoicacid, dodecanoic acid, tridecanoic acid, tetradecanoic acid,pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoicacid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, docosanoicacid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid,hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoicacid, triacontanoic acid, tetra-triacontanoic acid, pentatriacontanoicacid, hexatriacontanoic acid, alpha linolenic acid, eicosapentaenoicacid, docosahexaenoic acid, linolenic acid, gamma-linolenic acid,dihomo-gamma-linolenic acid, arachidonic acid, paullinic acid, oleicacid, elaidic acid, eicosenoic acid, erucic acid, nervonic acid, or acombination thereof.

The primary amine compound may include a pentylamine, hexylamine,heptylamine, octylamine, nonylamine, decylamine, undecylamine,dodecylamine, tridecylamine, pentadecylamine, hexadecylamine,heptadecylamine, ocatdecylamine, nonadecylamine, oleylamine, or acombination thereof.

The secondary amide compound may include the same or different twoaliphatic hydrocarbon groups. A carbon number of the aliphatichydrocarbon group may be greater than or equal to 7, for example,greater than or equal to 8, greater than or equal to 9, greater than orequal to 10, greater than or equal to 11, greater than or equal to 12,greater than or equal to 13, greater than or equal to 14, greater thanor equal to 15, greater than or equal to 16, greater than or equal to17, greater than or equal to 18, or greater than or equal to 19. Acarbon number of the aliphatic hydrocarbon group may be less than orequal to 40, less than or equal to 39, less than or equal to 38, lessthan or equal to 37, less than or equal to 36, less than or equal to 35,less than or equal to 34, less than or equal to 33, less than or equalto 32, less than or equal to 31, less than or equal to 30, less than orequal to 29, less than or equal to 28, less than or equal to 27, lessthan or equal to 26, or less than or equal to 25. The secondary amidecompound may have two different aliphatic hydrocarbon groups. In someembodiments, the aliphatic hydrocarbon group of the secondary amidecompound may include a branched or linear long chain alkyl, a branchedor linear long chain alkenyl, a branched or linear long chain alkynyl,or a combination thereof. As used herein, “long chain” refers to acarbon number of greater than or equal to 5, for example, at least 6, orat least 7.

A display device including a quantum dot based light emitting element isexpected to realize an improved brightness and an enhanced colorreproducibility. To this end, the quantum dot included in the elementmay be required to have an increased efficiency and a narrow FWHM. Forexample, it may be desired that the quantum dots may emit light of awavelength between about 450 nanometers (nm) and about 460 nm or betweenabout 520 and about 540 nm at a quantum efficiency of greater than orequal to about 80% and with a FWHM of less than or equal to about 40 nm.However, it is difficult or has not been reported yet to produce aquantum dot satisfying the foregoing desired conditions, for example, atan increased production yield.

According to the production method of the embodiments, a core particleis prepared in the presence of the aforementioned organic ligands, andthe core particle thus prepared may have a relatively uniform shape(e.g., a sphere) and a relatively uniform particle size distribution.Present inventors have found that a quantum dot may emit light of adesired wavelength with an increased quantum efficiency and a narrowFWHM when a shell is formed on the aforementioned core of theembodiments.

Without wishing to be bound by any theory, it is believed that an amideligand having a structure represented by Chemical Formula 1 (e.g.,having a wedge structure illustrated in FIG. 1) may readily andrelatively densely surround a zinc precursor at an early stage of areaction for forming the core, which enables a uniform and fastnucleation and makes it possible to stabilize the core. For example, itis believed that for the fast nucleation, forming a relatively labilezinc precursor may be necessary in order for the zinc precursor and theselenium precursor to readily combine and produce a ZnSe monomerconsistently. The amide ligand having the foregoing structure may couplethrough the oxygen atoms thereof with a zinc of the zinc precursor thatdoes not include oxygen while the nitrogen included in the amide mayalso coordinate thereto, forming a labile zinc precursor having an openarea (e.g., an open site). The formed nuclei may grow stably in thepresence of the wedge-type amide ligand, a carboxylic acid ligand, andan amine ligand, and this makes it possible to provide the core havingthe foregoing features. The zinc precursor may not include a zinc-oxygenbond.

In the organic ligand mixture, an amount of each component may bedetermined based on an amount of the zinc precursor. In someembodiments, based on 1 mole of the zinc precursor, an amount of thecarboxylic acid compound may be greater than or equal to about 0.1moles, for example, greater than or equal to about 0.2 moles, greaterthan or equal to about 0.3 moles, greater than or equal to about 0.4moles, greater than or equal to about 0.5 moles, greater than or equalto about 0.6 moles, greater than or equal to about 0.7 moles, greaterthan or equal to about 0.8 moles, greater than or equal to about 0.9moles, greater than or equal to about 1 mole, greater than or equal toabout 1.1 moles, greater than or equal to about 1.2 moles, greater thanor equal to about 1.3 moles, or greater than or equal to about 1.4moles. Based on 1 mole of the zinc precursor, an amount of thecarboxylic acid compound may be less than or equal to about 10 moles,for example, less than or equal to about 9 moles, less than or equal toabout 8 moles, less than or equal to about 7 moles, less than or equalto about 6 moles, less than or equal to about 5 moles, less than orequal to about 4 moles, less than or equal to about 3 moles, less thanor equal to about 2 moles.

Based on 1 mole of the zinc precursor, an amount of the primary aminecompound in the organic ligand mixture may be greater than or equal toabout 0.1 moles, for example, greater than or equal to about 0.2 moles,greater than or equal to about 0.3 moles, greater than or equal to about0.4 moles, greater than or equal to about 0.5 moles, greater than orequal to about 0.6 moles, greater than or equal to about 0.7 moles,greater than or equal to about 0.8 moles, greater than or equal to about0.9 moles, greater than or equal to about 1 moles, greater than or equalto about 1.1 moles, greater than or equal to about 1.2 moles, greaterthan or equal to about 1.3 moles, greater than or equal to about 1.4moles. Based on 1 mole of the zinc precursor, an amount of the primaryamine compound may be less than or equal to about 10 moles, for example,less than or equal to about 9 moles, less than or equal to about 8moles, less than or equal to about 7 moles, less than or equal to about6 moles, less than or equal to about 5 moles, less than or equal toabout 4 moles, less than or equal to about 3 moles, or less than orequal to about 2 moles.

Based on 1 mole of the zinc precursor, an amount of the secondary amidecompound in the organic ligand mixture may be greater than or equal toabout 0.1 moles, for example, greater than or equal to about 0.2 moles,greater than or equal to about 0.3 moles, greater than or equal to about0.4 moles, greater than or equal to about 0.5 moles, greater than orequal to about 0.6 moles, greater than or equal to about 0.7 moles,greater than or equal to about 0.8 moles, greater than or equal to about0.9 moles, greater than or equal to about 1 moles, greater than or equalto about 1.1 moles, greater than or equal to about 1.2 moles, greaterthan or equal to about 1.3 moles, or greater than or equal to about 1.4moles. Based on 1 mole of the zinc precursor, an amount of the secondaryamide compound may be less than or equal to about 10 moles, for example,less than or equal to about 9 moles, less than or equal to about 8moles, less than or equal to about 7 moles, less than or equal to about6 moles, less than or equal to about 5 moles, less than or equal toabout 4 moles, less than or equal to about 3 moles, or less than orequal to about 2 moles.

With respect to a total amount of the carboxylic acid ligand and theprimary amine ligand in the organic ligand mixture, an amount of thesecondary amide compound may be selected in light of reaction conditionssuch as a temperature, a time, and the like. For example, with respectto a total of 1 mole of the carboxylic acid ligand and the primary amineligand, an amount the secondary amide may be greater than or equal toabout 0.01 moles, for example, greater than or equal to about 0.05moles, greater than or equal to about 0.1 moles, or greater than orequal to about 0.2 moles. With respect to a total of 1 mole of thecarboxylic acid ligand and the primary amine ligand, an amount thesecondary amide may be less than or equal to about 1 mole, for example,less than or equal to about 0.9 moles, less than or equal to about 0.8moles, less than or equal to about 0.7 moles, less than or equal toabout 0.6 moles, less than or equal to about 0.5 moles, less than orequal to about 0.4 moles, less than or equal to about 0.3 moles, lessthan or equal to about 0.2 moles, or less than or equal to about 0.1moles. A molar ratio between the carboxylic acid ligand and the primaryamine ligand is not particularly limited and may be selectedappropriately. For example, a molar ratio between the carboxylic acidligand and the primary amine ligand (the carboxylic acid ligand: theprimary amine ligand) may be about 1:10 to about 1:0.1 (i.e., about 1:10to about 10:1).

In some embodiments, with respect to 1 mole of the carboxylic acidligand compound, an amount of the primary amine compound may be greaterthan or equal to about 0.1 moles, greater than or equal to about 0.2moles, greater than or equal to about 0.3 moles, greater than or equalto about 0.4 moles, greater than or equal to about 0.5 moles, greaterthan or equal to about 0.6 moles, greater than or equal to about 0.7moles, greater than or equal to about 0.8 moles, greater than or equalto about 0.9 moles, or greater than or equal to about 1 mole and lessthan or equal to about 10 moles, less than or equal to about 9 moles,less than or equal to about 8 moles, less than or equal to about 7moles, less than or equal to about 6 moles, less than or equal to about5 moles, less than or equal to about 4 moles, less than or equal toabout 3 moles, or less than or equal to about 2 moles. In someembodiments, the amount of the carboxylic acid ligand may be greaterthan the amount of the primary amine compound.

The organic ligand mixture may be prepared by mixing the carboxylic acidcompound, the primary amine compound, and the secondary amide compoundat the foregoing ratios.

In some embodiments, the organic ligand mixture may be prepared byheating the carboxylic acid compound and the primary amine compound inthe organic solvent at a temperature of greater than or equal to about200° C. (for example, greater than or equal to about 210° C., greaterthan or equal to about 220° C., greater than or equal to about 230° C.,greater than or equal to about 240° C., greater than or equal to about250° C., or greater than or equal to about 260° C.) for a predeterminedtime (for example, greater than or equal to about 5 minutes, greaterthan or equal to about 10 minutes, greater than or equal to about 15minutes, or greater than or equal to about 20 minutes) (hereinafter,also referred to as “in-situ synthesis of the ligand mixture”).

In the in-situ synthesis of the ligand mixture, an amount of the primaryamine compound may be greater than or equal to about 0.5 moles, forexample, greater than or equal to about 0.6 moles, greater than or equalto about 0.7 moles, greater than or equal to about 0.8 moles, greaterthan or equal to about 0.9 moles, or greater than or equal to about 1mole, with respect to 1 mole of the carboxylic acid compound.

In the in-situ synthesis of the ligand mixture, an amount of the primaryamine compound may be less than or equal to about 3 moles, for example,less than or equal to about 2.9 moles, less than or equal to about 2.8moles, less than or equal to about 2.7 moles, less than or equal toabout 2.6 moles, less than or equal to about 2.5 moles, less than orequal to about 2.3 moles, less than or equal to about 2.2 moles, lessthan or equal to about 2.1 moles, less than or equal to about 2.0 moles,less than or equal to about 1.9 moles, less than or equal to about 1.8moles, less than or equal to about 1.7 moles, less than or equal toabout 1.6 moles, less than or equal to about 1.5 moles, with respect to1 mole of the carboxylic acid compound. In the in-situ synthesis of theligand mixture, the carboxylic acid compound may be used in an amountthat is greater than that of the primary amine compound.

The first organic solvent is not particularly limited and may beselected appropriately. The first organic solvent may include asecondary amine having at least one (e.g., one or two same or different)C6 to C40 aliphatic hydrocarbon groups (e.g., alkyl, alkenyl, oralkynyl) such as dioctylamine, dinonylamine, or the like, a tertiaryamine having at least one (e.g., one, or two, or three same ordifferent) C6 to C40 aliphatic hydrocarbon groups (e.g., alkyl, alkenyl,or alkynyl) such as a trioctyl amine, a nitrogen-containing heterocycliccompound such as pyridine, a C6 to C50 aliphatic hydrocarbon (e.g., C6to C40 alkene or olefin solvent such as octadecene, or a C6 to C40alkane such as hexadecane, octadecane, or squalane), an aromatichydrocarbon (e.g., an aryl substituted with a C1 to C24 (C6 to C24)alkyl group (e.g., phenyldodecane, phenyltetradecane, or phenylhexadecane), a primary, secondary, or tertiary phosphine (e.g., trioctylphosphine) with at least one (e.g., 1, 2, or 3) same or different C6 toC22 alkyl group, a primary, secondary, or tertiary phosphine oxide(e.g., trioctylphosphine oxide) substituted with at least one (e.g., 1,2, or 3) same or different C6 to C22 alkyl group, a C12 to C22 aromaticether such as a phenyl ether or a benzyl ether, or a combinationthereof.

In the organic ligand mixture, an amount of the organic solvent may beselected appropriately in light of the amount of the precursor set forthbelow and is not particularly limited.

The organic ligand mixture thus prepared is heated in an inertatmosphere at a first temperature to obtain a heated organic ligandmixture. The first temperature may be greater than or equal to about240° C., for example, greater than or equal to about 245° C., greaterthan or equal to about 250° C., greater than or equal to about 255° C.,greater than or equal to about 260° C., greater than or equal to about265° C., greater than or equal to about 270° C., or greater than orequal to about 275° C. The first temperature may be less than or equalto about the first reaction temperature that will be described below.

To the heated organic ligand mixture, a zinc precursor, a seleniumprecursor, and optionally a tellurium precursor are added to provide areaction mixture. The zinc precursor may not include oxygen. Theselenium precursor may not include oxygen. If present, the telluriumprecursor may not include oxygen.

The zinc precursor may include a Zn powder (i.e., Zn metal), analkylated Zn compound (e.g., a C2 to C30 alkylated (e.g., dialkylated)zinc such as dimethyl zinc, diethyl zinc), a Zn halide (e.g., zincchloride, zinc bromide, zinc iodide, or the like), a Zn cyanide, or acombination thereof.

The selenium precursor may include an organic dispersion of a seleniumelement in an organic solvent such as amines, phosphines, or phosphineoxide solvent. For example, the selenium precursor may includeselenium-trioctylphosphine (Se-TOP), selenium-tributylphosphine(Se-TBP), selenium-triphenylphosphine (Se-TPP),selenium-diphenylphosphine (Se-DPP), or a combination thereof.

The tellurium precursor may include an organic dispersion of a telluriumelement in an organic solvent such as amines, phosphines, or phosphineoxide solvent. The tellurium precursor may includetellurium-trioctylphosphine (Te-TOP), tellurium-tributylphosphine(Te-TBP), tellurium-triphenylphosphine (Te-TPP),tellurium-diphenylphosphine (Te-DPP), or a combination thereof.

An amount of the selenium precursor for forming the core may be greaterthan or equal to about 20 moles, for example, greater than or equal toabout 25 moles, greater than or equal to about 26 moles, greater than orequal to about 27 moles, greater than or equal to about 28 moles,greater than or equal to about 29 moles, greater than or equal to about30 moles, greater than or equal to about 31 moles, greater than or equalto about 32 moles, greater than or equal to about 33 moles, greater thanor equal to about 34 moles, greater than or equal to about 35 moles,greater than or equal to about 36 moles, greater than or equal to about37 moles, greater than or equal to about 38 moles, greater than or equalto about 39 moles, or greater than or equal to about 40 moles, based onone mole of the tellurium precursor. The amount of the seleniumprecursor may be less than or equal to about 60 moles, less than orequal to about 59 moles, less than or equal to about 58 moles, less thanor equal to about 57 moles, less than or equal to about 56 moles, orless than or equal to about 55 moles, based on one mole of the telluriumprecursor.

The reaction mixture may be heated and kept at a first reactiontemperature to synthesize a core particle.

The first reaction temperature may be greater than or equal to about270° C., for example, greater than or equal to about 280° C., greaterthan or equal to about 290° C., or greater than or equal to about 300°C. The first reaction temperature may be less than or equal to about350° C., for example, less than or equal to about 340° C., less than orequal to about 330° C., or less than or equal to about 320° C. The firstreaction temperature may be greater than the first temperature. Areaction time for forming the core is not particularly limited and maybe appropriately selected. For example, the reaction time may be greaterthan or equal to about 5 minutes, greater than or equal to about 10minutes, greater than or equal to about 15 minutes, greater than orequal to about 20 minutes, greater than or equal to about 25 minutes,greater than or equal to about 30 minutes, greater than or equal toabout 35 minutes, greater than or equal to about 40 minutes, greaterthan or equal to about 45 minutes, or greater than or equal to about 50minutes, but is not limited thereto. For example, the reaction time maybe less than or equal to about 2 hours, but is not limited thereto. Bycontrolling the reaction time, the size of the core, i.e. the firstsemiconductor nanocrystal particle, may be controlled.

In some embodiments, for controlling a particle size of the core, a zinccontaining compound and/or the aforementioned selenium precursor may befurther added during the reaction (for example, during the heating ofthe reaction mixture at the first reaction temperature). Examples of thezinc containing compound includes a reaction product (e.g., zinc oleate)of the aforementioned zinc precursor and the organic ligand (e.g., theoleic acid).

In an embodiment, a selenium containing compound derived from theaforementioned selenium precursors may be added during the reaction. Instill another embodiment, a tellurium containing compound derived fromthe aforementioned tellurium precursors may be added during thereaction.

The core particle, i.e. the first semiconductor nanocrystal particle,may include ZnSe_(1−x)Te_(x) (wherein, x is greater than 0 and less thanor equal to about 0.2). In some embodiments, the core may include a ZnSebased material further including a small amount of tellurium. The coreparticle may have a cubic (zinc blend) crystal structure. For example,the core may include ZnTe_(x)Se_(1−x), wherein, x is greater than 0, forexample, greater than or equal to about 0.001, and less than or equal toabout 0.2, for example, less than or equal to about 0.1, less than orequal to about 0.09, less than or equal to about 0.08, less than orequal to about 0.07, less than or equal to about 0.06, or less than orequal to about 0.05. The maximum wavelength of the light emission peakof the semiconductor nanocrystal particle may be increased by increasinga ratio of an amount of tellurium relative to an amount of selenium inthe core.

In the core, an amount of the tellurium may be greater than or equal toabout 0.001 moles, greater than or equal to about 0.005 moles, greaterthan or equal to about 0.006 moles, greater than or equal to about 0.007moles, greater than or equal to about 0.008 moles, greater than or equalto about 0.009 moles, greater than or equal to about 0.01 moles, orgreater than or equal to about 0.02 moles, based on one mole of theselenium. In the core, an amount of the tellurium may be less than orequal to about 0.053 moles, for example, less than or equal to about0.05 moles, less than or equal to about 0.049 moles, less than or equalto about 0.048 moles, less than or equal to about 0.047 moles, less thanor equal to about 0.046 moles, less than or equal to about 0.045 moles,less than or equal to about 0.044 moles, less than or equal to about0.043 moles, less than or equal to about 0.042 moles, less than or equalto about 0.041 moles, or less than or equal to about 0.04 moles, basedon one mole of the selenium.

Without wishing to be bound by any particular theory, the core may havevarious forms in terms of distributions of Zn, Se, and Te.

The (average) size of the core may be greater than or equal to about 2nanometers (nm), greater than or equal to about 3 nm, or greater than orequal to about 4 nm. The (average) particle size of the core may be lessthan or equal to about 6 nm, for example less than or equal to about 5nm.

The method may further include forming a shell including a secondsemiconductor nanocrystal material on the core. The formation of theshell may include providing a first shell precursor solution including ametal-containing first shell precursor, an organic ligand, and a secondorganic solvent;

providing a second shell precursor including a non-metal element; and

heating the first shell precursor solution at a second reactiontemperature and adding (or injecting) the first semiconductornanocrystal particle and the second shell precursor thereto to conduct areaction between the first shell precursor and the second shellprecursor. By the reaction between the first and second shellprecursors, the shell including the second semiconductor nanocrystalmaterial may be disposed on at least a portion of a core surface.

The first shell precursor may include zinc. For example, the first shellprecursor may be a zinc or a zinc compound. The second shell precursormay include selenium, sulfur, or a combination thereof. For example, thesecond shell precursor may be a selenium element or compound, a sulfurelement or compound, or a combination thereof. The second semiconductornanocrystal material may include zinc (Zn), selenium (Se), and sulfur(S).

The zinc precursor for the formation of the shell may include a Znpowder, an alkylated Zn compound (e.g., C2 to C30 alkyl (e.g., dialkyl)zinc such as dimethyl zinc, diethyl zinc), a Zn alkoxide (e.g., a zincethoxide), a Zn carboxylate (e.g., a zinc acetate or zinc aliphaticcarboxylate, for example, zinc long chain aliphatic carboxylate such aszinc oleate), a Zn nitrate, a Zn perchlorate, a Zn sulfate, a Znacetylacetonate, a Zn halide (e.g., a zinc chloride), a Zn cyanide, a Znhydroxide, ZnO, a zinc peroxide, or a combination thereof. Examples ofthe first shell precursor may include a zinc carboxylate having a longalkyl chain such as zinc oleate or zinc stearate, dimethyl zinc, diethylzinc, zinc acetate, zinc acetylacetonate, zinc iodide, zinc bromide,zinc chloride, zinc fluoride, zinc carbonate, zinc cyanide, zincnitrate, zinc oxide, zinc peroxide, zinc perchlorate, zinc sulfate, or acombination thereof.

Details of the selenium precursor are the same as set forth above.

The sulfur precursor may be hexane thiol, octane thiol, decane thiol,dodecane thiol, hexadecane thiol, mercapto propyl silane,sulfur-trioctylphosphine (S-TOP), sulfur-tributylphosphine (S-TBP),sulfur-triphenylphosphine (S-TPP), sulfur-trioctylamine (S-TOA),bistrimethylsilyl sulfur, ammonium sulfide, sodium sulfide, or acombination thereof.

In an embodiment, after core synthesis and during a shell growth, asolution including the shell precursors may be added to a reactionsystem over several times (e.g., in stages) in order for a compositionof the shell to be changed or varied (e.g., in a radial direction). Asnon-limiting examples, in a case in which a shell of a ternary element(ABC) compound is formed, the sequence of the addition of theprecursors, the amount of the precursors, and the reaction duration forthe precursors (e.g., the A element precursor (e.g., a metal elementsuch as Zn), the B element precursor (e.g., a first non-metal elementsuch as selenium), the C element precursor (e.g., a second non-metalelement such as sulfur) solutions) may be adjusted. For example, thecore is added to the A element precursor solution, the B elementprecursor solution is added thereto, and then a reaction is performedfor a predetermined time. Subsequently, at least one of the C elementprecursor solution and the B element precursor solution may be added tothe reaction system in a form of a mixture or individually and then areaction is performed. Herein, addition timing and the reaction time ofthe C element precursor solution and the B element precursor solutionand a ratio of these precursors in the reaction system may becontrolled.

A lattice mismatch at an interface of the core and shell may becontrolled by controlling the addition times and the addition timing ofthe C element precursor solution and the B element precursor solutionand a ratio of the precursors in the reaction system. In addition,growth energy at the surface may be controlled by changing a reactiontemperature and, for example, a kind of, the C element precursor.

The organic ligand (e.g., for the formation of the shell) may coordinateto, e.g., be bound to, the surface of the produced nanocrystal particle(or the quantum dot) and may have an effect on the luminous andelectrical properties thereof as well as may effectively disperse thequantum dots in a solution phase. The organic ligand may include RCOOH,RNH₂, R₂NH, R₃N, RSH, RH₂PO, R₂HPO, R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR,RHPOOH, RPO(OH)₂, R₂POOH (wherein, R is the same or different and isindependently include a C1 to C40 substituted or unsubstituted aliphatichydrocarbon group, C6 to C40 substituted or unsubstituted aromatichydrocarbon group, or a combination thereof), or a combination thereof.The ligand may be may be used alone or in a mixture of two or morecompounds.

Examples of the organic ligand compound may include methanethiol,ethanethiol, propanethiol, butanethiol, pentane thiol, hexanethiol,octanethiol, dodecanethiol, hexadecanethiol, octadecane thiol,benzylthiol; methylamine, ethylamine, propylamine, butylamine,pentylamine, hexylamine, octylamine, dodecylamine, hexadecylamine,oleylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine,methanoic acid, ethanoic acid, propanoic acid, butanoic acid, pentanoicacid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoic acid,hexadecanoic acid, octadecanoic acid, oleic acid, benzoic acid, palmiticacid, stearic acid; phosphine such as methylphosphine, ethylphosphine,propylphosphine, butylphosphine, pentylphosphine, tributylphosphine, ortrioctylphosphine, a phosphine oxide compound such as methylphosphineoxide, ethylphosphine oxide, propylphosphine oxide, butylphosphineoxide, or trioctylphosphine oxide; a diphenylphosphine ortriphenylphosphine compound, or an oxide compound thereof; phosphonicacid, or the like, but are not limited thereto. The organic ligandcompound may be used alone or in a mixture of two or more compounds. Inan embodiment, the organic ligand compound may be a combination of RCOOHand amine (e.g., RNH₂, R₂NH, and/or R₃N).

The second organic solvent may be a C6 to C40 (e.g., C6 to C22) primaryamine such as a hexadecylamine (i.e., a primary amine having at leastone C6 to C40 (aliphatic) hydrocarbon group), a C6 to C40 (e.g., C6 toC22) secondary amine such as dioctylamine (i.e., a secondary aminehaving at least one C6 to C40 (aliphatic) hydrocarbon group), a C6 toC40 tertiary amine such as a trioctyl amine (i.e., a tertiary aminehaving at least one C6 to C40 (aliphatic) hydrocarbon group), anitrogen-containing heterocyclic compound such as pyridine, a C6 to C40olefin such as octadecene, a C6 to C40 aliphatic hydrocarbon such ashexadecane, octadecane, or squalane, a C6 to C50 aromatic hydrocarbon,an aromatic hydrocarbon substituted with a C6 to C30 (aliphatic)hydrocarbon group (e.g., alkyl group) such as phenyldodecane,phenyltetradecane, or phenyl hexadecane, a phosphine compound such as aprimary, secondary, or tertiary phosphine (e.g., trioctyl phosphine)substituted with at least one (e.g., 1, 2, or 3) C6 to C22 (aliphatic)hydrocarbon group (e.g., alkyl or alkenyl), a phosphine oxide compoundsuch as a primary, secondary, or tertiary phosphine oxide (e.g.,trioctylphosphine oxide) substituted with at least one (e.g., 1, 2, or3) C6 to C22 (aliphatic) hydrocarbon group (e.g., alkyl or alkenyl), aC12 to C22 aromatic ether such as a phenyl ether or a benzyl ether, or acombination thereof.

Reaction conditions (e.g., a reaction temperature or time) for the shellformation are not particularly limited and may be selectedappropriately. In a non-limiting example embodiment, under a vacuum, asolvent and optionally the ligand compound are heated (orvacuum-treated) at a predetermined temperature (e.g., greater than orequal to about 100° C.), and are heated again at predeterminedtemperature (e.g., greater than or equal to about 100° C.) under aninert gas atmosphere. Then, the core is injected, the shell precursorsare sequentially or simultaneously added, and then heated at apredetermined reaction temperature to conduct a reaction. Mixtures eachincluding the shell precursors at a different ratio may be sequentiallyinjected during the reaction time.

After the completion of the reaction, a non-solvent is added to reactionproducts and the nanocrystal particles coordinated with, e.g., bound to,the ligand compound may be separated. The non-solvent may be a polarsolvent that is miscible with the solvent used in the core formationand/or shell formation reactions and is not capable of dispersing theproduced nanocrystals therein. The non-solvent may be selected dependingthe solvent used in the reaction and may be for example acetone,ethanol, butanol, isopropanol, ethanediol, water, tetrahydrofuran (THF),dimethylsulfoxide (DMSO), diethylether, formaldehyde, acetaldehyde, asolvent having a similar solubility parameter to the foregoing solvents,or a combination thereof. Separation of the nanocrystal particles mayinvolve centrifugation, sedimentation, chromatography, or distillation.The separated nanocrystal particles may be added to a washing solventand washed, if desired. Types of the washing solvent are notparticularly limited and a solvent having similar solubility parameterto that of the ligand may be used and examples thereof may includehexane, heptane, octane, chloroform, toluene, benzene, or the like.

In other embodiments, a quantum dot includes a core including a firstsemiconductor nanocrystal material including zinc, tellurium, andselenium and a shell disposed on at least a portion of the core andincluding a second semiconductor nanocrystal material different from thefirst semiconductor nanocrystal material. The quantum dot does notinclude cadmium. A maximum photoluminescent emission peak of the quantumdot is in a wavelength region between about 440 nanometers (nm) to 540nm. The quantum dot exhibits a quantum efficiency of greater than orequal to about 60%. The first semiconductor nanocrystal material mayinclude ZnTe_(x)Se_(1−x) (wherein, x is greater than about 0 and lessthan or equal to about 0.2).

Details of the core are the same as set forth above.

In the quantum dot, a ratio of a mole amount (i.e., molar amount) of thetellurium with respect to that of selenium (e.g., measured byinductively coupled plasma-atomic emission spectroscopy (ICP-AES)) maybe less than or equal to about 0.1, less than or equal to about 0.09,less than or equal to about 0.08, less than or equal to about 0.07, lessthan or equal to about 0.06, less than or equal to about 0.05, less thanor equal to about 0.049, less than or equal to about 0.048, less than orequal to about 0.047, less than or equal to about 0.045, less than orequal to about 0.044, less than or equal to about 0.043, less than orequal to about 0.042, less than or equal to about 0.041, less than orequal to about 0.04, less than or equal to about 0.039, less than orequal to about 0.035, less than or equal to about 0.03, less than orequal to about 0.029, less than or equal to about 0.025, less than orequal to about 0.024, less than or equal to about 0.023, less than orequal to about 0.022, less than or equal to about 0.021, less than orequal to about 0.02, less than or equal to about 0.019, less than orequal to about 0.018, less than or equal to about 0.017, less than orequal to about 0.016, less than or equal to about 0.015, less than orequal to about 0.014, less than or equal to about 0.013, less than orequal to about 0.012, less than or equal to about 0.011, or less than orequal to about 0.01. A ratio of a mole amount of the tellurium withrespect to that of selenium may be 0.001, greater than or equal to about0.002, greater than or equal to about 0.003, greater than or equal toabout 0.004, greater than or equal to about 0.005, greater than or equalto about 0.006, or greater than or equal to about 0.007. A mole ratio ofthe tellurium with respect to the selenium may be from about 0.004 toabout 0.025.

In the quantum dot, an amount (e.g., a mole amount) of the zinc may begreater than that of the selenium. In the quantum dot, (for example,when determined by ICP-AES) a mole ratio of the tellurium with respectto the zinc may be less than or equal to about 0.02, less than or equalto about 0.019, less than or equal to about 0.018, less than or equal toabout 0.017, less than or equal to about 0.016, less than or equal toabout 0.015, less than or equal to about 0.014, less than or equal toabout 0.013, less than or equal to about 0.012, less than or equal toabout 0.011, less than or equal to about 0.011, less than or equal toabout 0.01, less than or equal to about 0.009, less than or equal toabout 0.008, less than or equal to about 0.007, or less than or equal toabout 0.006.

In the quantum dot, (for example, when being determined by ICP-AES) amole ratio of the tellurium with respect to the zinc may be greater thanor equal to about 0.0001, greater than or equal to about 0.0005, orgreater than or equal to about 0.001.

In the quantum dot, (for example, when being determined by ICP-AES), anamount (e.g., a mole amount) of the zinc may be greater than that of theselenium, and an amount (e.g., a mole amount) of the selenium may begreater than that of the tellurium.

For example, in the ICP-AES analysis, a mole ratio of the selenium withrespect to the zinc may be less than 1, for example, less than or equalto about 0.95, less than or equal to about 0.90, less than or equal toabout 0.85, or less than or equal to about 0.8.

For example, in the ICP-AES analysis, a mole ratio of the tellurium withrespect to the zinc may be less than or equal to about 0.03, forexample, less than or equal to about 0.027, less than or equal to about0.025, less than or equal to about 0.02, less than or equal to about0.019, less than or equal to about 0.018, less than or equal to about0.017, 0.016, less than or equal to about 0.015, less than or equal toabout 0.01, less than or equal to about 0.009, less than or equal toabout 0.008, less than or equal to about 0.007, less than or equal toabout 0.006, or less than or equal to about 0.005. A mole ratio of thetellurium with respect to the zinc may be greater than or equal to about0.001, greater than or equal to about 0.002, or greater than or equal toabout 0.003. In the quantum dot of some embodiments, an amount of thetellurium may be less than or equal to about 1 wt % with respect to atotal weight of the quantum dot.

In the quantum dots, a mole ratio of the sulfur with respect to the zincmay be greater than or equal to about 0.1, for example, greater than orequal to about 0.15, or greater than or equal to about 0.2. In thequantum dots, a mole ratio of the sulfur with respect to the zinc may beless than or equal to about 0.5, for example, less than or equal toabout 0.45. In the quantum dots, a mole ratio of a sum of the sulfur andthe selenium (S+Se) with respect to the zinc may be greater than orequal to about 0.3, greater than or equal to about 0.4, or greater thanor equal to about 0.5. In the quantum dots, a mole ratio of a sum of thesulfur and the selenium (S+Se) with respect to the zinc may be less thanor equal to about 1, for example, less than or equal to about 1.

The quantum dot may include various shapes. The semiconductornanocrystal may include a spherical shape, a polygonal shape, a multipodshape, or a combination thereof. In an embodiment, the semiconductornanocrystal particle may have a multipod shape. The multipod may have atleast two (e.g., at least three or at least four) branch parts and avalley part therebetween. A size (e.g., an average size) of thesemiconductor nanocrystal particle may be greater than or equal to about3 nm, for example greater than or equal to about 4 nm, greater than orequal to about 5 nm, or greater than or equal to about 6 nm. The size ofthe semiconductor nanocrystal may be less than or equal to about 50 nm,for example less than or equal to about 45 nm, less than or equal toabout 40 nm, less than or equal to about 35 nm, less than or equal toabout 30 nm, less than or equal to about 25 nm, less than or equal toabout 24 nm, less than or equal to about 23 nm, less than or equal toabout 22 nm, less than or equal to about 21 nm, less than or equal toabout 20 nm, less than or equal to about 19 nm, less than or equal toabout 18 nm, less than or equal to about 17 nm, or less than or equal toabout 16 nm. Herein, when the semiconductor nanocrystal particle has aspherical shape, the size of the semiconductor nanocrystal may be adiameter. When the quantum dot is a non-spherically shaped particle, itssize may be a diameter calculated from a two dimensional area of anelectron microscopic image of the particle. The size of thesemiconductor nanocrystal particle (or the core) may be determined byfor example, a Transmission Electron Microscopic analysis, but it is notlimited thereto.

The quantum dots of the embodiments may emit blue light having a maximumphotoluminescence peak at a wavelength of greater than or equal to about430 nm (for example, 440 nm, or greater than or equal to about 450 nm)and less than or equal to about 470 nm (for example, less than about 470nm, or less than or equal to about 460 nm). The blue light may have amaximum luminous peak wavelength of from about 450 nm to about 460 nm.

The quantum dots of the embodiments may emit green light having amaximum photoluminescence peak at a wavelength of greater than or equalto about 500 nm (for example, greater than or equal to about 510 nm, orgreater than or equal to about 520 nm) and less than or equal to about560 nm (for example, less than or equal to about 550 nm, or less than orequal to about 540 nm). The green light may have a maximum luminous peakwavelength of from about 520 nm to about 540 nm.

The maximum luminous peak may have a FWHM of less than or equal to about50 nm, for example, less than or equal to about 49 nm, less than orequal to about 48 nm, less than or equal to about 47 nm, less than orequal to about 46 nm, less than or equal to about 45 nm, less than orequal to about 44 nm, less than or equal to about 43 nm, less than orequal to about 42 nm, less than or equal to about 41 nm, less than orequal to about 40 nm, less than or equal to about 39 nm, less than orequal to about 38 nm, less than or equal to about 37 nm, less than orequal to about 36 nm, less than or equal to about 35 nm, less than orequal to about 34 nm, less than or equal to about 33 nm, less than orequal to about 32 nm, less than or equal to about 31 nm, less than orequal to about 30 nm, less than or equal to about 29 nm, or less than orequal to about 28 nm.

The quantum dots may have a quantum efficiency of greater than or equalto about 60%, for example, greater than or equal to about 61%, greaterthan or equal to about 62%, greater than or equal to about 63%, greaterthan or equal to about 64%, greater than or equal to about 65%, greaterthan or equal to about 66%, greater than or equal to about 67%, greaterthan or equal to about 68%, greater than or equal to about 69%, orgreater than or equal to about 70%. The quantum dots may have quantumefficiency of greater than or equal to about 80%, greater than or equalto about 90%, greater than or equal to about 95%, greater than or equalto about 99%, or about 100%.

In an embodiment, an electronic device includes the quantum dots of theembodiments. The device may include a display device, a light emittingdiode (LED), an organic light emitting diode (OLED), a quantum dot LED,a sensor, a solar cell, an image sensor, or a liquid crystal display(LCD), but is not limited thereto.

In an embodiment, the electronic device may be a LCD device, aphotoluminescent element (e.g., a quantum dot sheet, a quantum dot rail,a lighting device), an electroluminescent device (e.g., QD LED), or abacklight unit.

In a non-limiting embodiment, the electronic device may include aquantum dot sheet and the quantum dots of the embodiments may beincluded in the quantum dot sheet (e.g., in a form of a semiconductornanocrystal-polymer composite).

In a non-limiting embodiment, the electronic device may be anelectroluminescent device. The electronic device may include an anode 1and a cathode 5 facing each other and a quantum dot emission layer 3disposed between the anode and the cathode and including a plurality ofquantum dots, and the plurality of quantum dots may include the bluelight emitting semiconductor nanocrystal particle (see FIG. 2).

The cathode may include an electron injection conductor (for example,having a relatively low work function). The anode may include a holeinjection conductor (for example, having a relatively high workfunction). The electron/hole injection conductors may include a metal(e.g., aluminum, magnesium, tungsten, nickel, cobalt, platinum,palladium, calcium, or LiF), a metal compound, an alloy, or acombination thereof; a metal oxide such as gallium indium oxide orindium tin oxide; or a conductive polymer such as polyethylenedioxythiophene (e.g., having a relatively high work function), but arenot limited thereto.

At least one of the cathode and the anode may be a light transmittingelectrode or a transparent electrode. In an embodiment, both of theanode and the cathode may be light transmitting electrodes. Theelectrode may be patterned.

The light transmitting electrode may include, for example, a transparentconductor such as indium tin oxide (ITO) or indium zinc oxide (IZO),gallium indium tin oxide, zinc indium tin oxide, titanium nitride,polyaniline, or LiF/Mg:Ag, or a metal thin film of a thin monolayer ormultilayer, but is not limited thereto. When one of the cathode and theanode is a non-light transmitting electrode, it may include, forexample, an opaque conductor such as aluminum (Al), a lithium aluminum(Li:Al) alloy, a magnesium-silver alloy (Mg:Ag), or a lithiumfluoride-aluminum (LiF:Al).

The light transmitting electrode may be disposed on a transparentsubstrate (e.g., insulating transparent substrate). The substrate may berigid or flexible. The substrate may be a plastic, glass, or a metal.

Thicknesses of the anode and the cathode are not particularly limitedand may be selected considering device efficiency. For example, thethickness of the anode (or the cathode) may be greater than or equal toabout 5 nm, for example, greater than or equal to about 50 nm, but isnot limited thereto. For example, the thickness of the anode (or thecathode) may be less than or equal to about 100 micrometers (μm), forexample, less than or equal to about 10 μm, less than or equal to about1 μm, less than or equal to about 900 nm, less than or equal to about500 nm, or less than or equal to about 100 nm, but is not limitedthereto.

The quantum dot emission layer includes a plurality of quantum dots. Theplurality of quantum dots includes the blue light emitting semiconductornanocrystal particle according to the aforementioned embodiments. Thequantum dot emission layer may include a monolayer of the blue lightemitting semiconductor nanocrystal particles.

The quantum dot emission layer may be formed by preparing a dispersionincluding the quantum dots dispersed in a solvent, applying thedispersion via spin coating, ink jet coating, or spray coating, anddrying the same. The emissive layer may have a thickness of greater thanor equal to about 5 nm, for example, greater than or equal to about 10nm, greater than or equal to about 15 nm, greater than or equal to about20 nm, or greater than or equal to about 25 nm, and less than or equalto about 200 nm, for example, less than or equal to about 150 nm, lessthan or equal to about 100 nm, less than or equal to about 90 nm, lessthan or equal to about 80 nm, less than or equal to about 70 nm, lessthan or equal to about 60 nm, less than or equal to about 50 nm, lessthan or equal to about 40 nm, or less than or equal to about 30 nm.

The electronic device may include charge (hole or electron) auxiliarylayers between the anode and the cathode. For example, as shown in FIG.2, the electronic device may include a hole auxiliary layer 2 or anelectron auxiliary layer 4 between the anode and the quantum dotemission layer and/or between the cathode and the quantum dot emissionlayer.

In the figures, the electron/hole auxiliary layer is formed as a singlelayer, but it is not limited thereto and may include a plurality oflayers including at least two stacked layers.

The hole auxiliary layer may include for example a hole injection layer(HIL) to facilitate hole injection, a hole transport layer (HTL) tofacilitate hole transport, an electron blocking layer (EBL) to inhibitelectron transport, or a combination thereof. For example, the holeinjection layer may be disposed between the hole transport layer and theanode. For example, the electron blocking layer may be disposed betweenthe emission layer and the hole transport (injection) layer, but is notlimited thereto. A thickness of each layer may be selectedappropriately. For example, a thickness of each layer may be greaterthan or equal to about 1 nm, greater than or equal to about 5 nm,greater than or equal to about 10 nm, greater than or equal to about 15nm, greater than or equal to about 20 nm, or greater than or equal toabout 25 nm, and less than or equal to about 500 nm, less than or equalto about 400 nm, less than or equal to about 300 nm, less than or equalto about 200 nm, less than or equal to about 100 nm, less than or equalto about 90 nm, less than or equal to about 80 nm, less than or equal toabout 70 nm, less than or equal to about 60 nm, or less than or equal toabout 50 nm, but is not limited thereto. The hole injection layer may bean organic layer that is formed by a solution process (e.g., spincoating etc.) such as PEDOT:PSS. The hole transport layer may be anorganic layer that is formed by a solution process (e.g., spin coatingetc.).

The electron auxiliary layer may include for example an electroninjection layer (EIL) to facilitate electron injection, an electrontransport layer (ETL) to facilitate electron transport, a hole blockinglayer (HBL) to inhibit hole transport, or a combination thereof. Forexample, the electron injection layer may be disposed between theelectron transport layer and the cathode. For example, the hole blockinglayer may be disposed between the emission layer and the electrontransport (injection) layer, but is not limited thereto. A thickness ofeach layer may be selected appropriately. For example, a thickness ofeach layer may be greater than or equal to about 1 nm, greater than orequal to about 5 nm, greater than or equal to about 10 nm, greater thanor equal to about 15 nm, greater than or equal to about 20 nm, orgreater than or equal to about 25 nm, and less than or equal to about500 nm, less than or equal to about 400 nm, less than or equal to about300 nm, less than or equal to about 200 nm, less than or equal to about100 nm, less than or equal to about 90 nm, less than or equal to about80 nm, less than or equal to about 70 nm, less than or equal to about 60nm, less than or equal to about 50 nm, but is not limited thereto. Theelectron injection layer may be an organic layer formed by deposition(e.g., vapor deposition). The electron transport layer may include aninorganic oxide or a (nano or fine) particles thereof or may include anorganic layer formed by deposition.

The quantum dot emission layer may be disposed in or on the holeinjection (or transport) layer or an electron injection (or transport)layer. The quantum dot emission layer may be disposed as a separatelayer between the hole auxiliary layer and the electron auxiliary layer.

The charge auxiliary layer, the electron blocking layer, and the holeblocking layer may include for example an organic material, an inorganicmaterial, or an organic/inorganic material. The organic material may bea compound having hole or electron-related properties. The inorganicmaterial may be for example a metal oxide such as molybdenum oxide,tungsten oxide, zinc oxide, or nickel oxide, but is not limited thereto.

The hole transport layer (HTL) and/or the hole injection layer mayinclude, each independently, for examplepoly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS),poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB),polyarylamine, poly(N-vinylcarbazole, PVK), polyaniline, polypyrrole,N,N,N′,N′-tetrakis (4-methoxyphenyl)-benzidine (TPD),4,4′,-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA(4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine),4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA),1,1-bis[(di-4-tolylamino)phenylcyclohexane (TAPC), a p-type metal oxide(e.g., NiO, WO₃, MoO₃, etc.), p-type metal sulfide (e.g., ZnS), acarbonaceous material such as graphene oxide, or a combination thereof,but is not limited thereto.

The electron blocking layer (EBL) may include for examplepoly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS),poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB)polyarylamine, poly(N-vinylcarbazole), polyaniline, polypyrrole,N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine (TPD),4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA,4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA), or a combinationthereof, but is not limited thereto.

The electron transport layer (ETL) and/or the electron injection layer(EIL) may, each independently, include for example1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA), bathocuproine(BCP), tris[3-(3-pyridyl)-mesityl]borane (3TPYMB), LiF, Alq₃, Gaq₃,Inq₃, Znq₂, Zn(BTZ)₂, BeBq₂, ET204(8-(4-(4,6-di(naphthalen-2-yl)-1,3,5-triazin-2-yl)phenyl)quinolone),8-hydroxyquinolinato lithium (Liq), an n-type metal oxide (e.g., ZnO,HfO₂, etc.), or a combination thereof, but is not limited thereto. Then-type metal oxide may be (crystalline) nanoparticles. The electrontransport layer (ETL) may include crystalline nanoparticles including azinc oxide compound (e.g., ZnO).

The hole blocking layer (HBL) may include for example1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA), bathocuproine(BCP), tris[3-(3-pyridyl)-mesityl] borane (3TPYMB), LiF, Alq₃, Gaq₃,Inq₃, Znq₂, Zn(BTZ)₂, BeBq₂, or a combination thereof, but is notlimited thereto.

In the foregoing “q” is 8-hydroxyquinoline, “BTZ” is2-(2-hydroxyphenyl)benzothiazolate, and “Bq” is10-hydroxybenzo[h]quinoline. The n-type metal oxide may be crystalline.

A device according to an embodiment as shown in FIG. 3 may have a normalstructure. In the device, an anode 10 disposed on a transparentsubstrate 100 may include a metal oxide transparent electrode (e.g., ITOelectrode) and a cathode 50 facing the anode may include a metal (Mg,Al, etc.) of a predetermined (e.g., relatively low) work function. Forexample, a hole auxiliary layer 20 (e.g., a hole transport layerincluding TFB and/or PVK and/or a hole injection layer includingPEDOT:PSS and/or a p-type metal oxide) may be disposed between thetransparent electrode 10 and the emission layer 30. An electronauxiliary layer (e.g., electron transport layer) 40 may be disposedbetween the quantum dot emission layer 30 and the cathode 50.

A device according to an embodiment as shown in FIG. 4 has an invertedstructure. In the device of the embodiments, a cathode 50 disposed on atransparent substrate 100 may include a metal oxide transparentelectrode (e.g., ITO) and an anode 10 facing the cathode may include ametal (e.g., Au, Ag, etc.) of a predetermined (e.g., relatively high)work function. For example, an n-type metal oxide (ZnO) may be disposedbetween the transparent electrode 50 and the emission layer 30 as anelectron auxiliary layer (e.g., an electron transport layer) 40. A holeauxiliary layer 20 (e.g., a hole transport layer including TFB and/orPVK and/or a hole injection layer including MoO₃ or another p-type metaloxide) may be disposed between the metal anode 10 and the quantum dotemission layer 30. Hereinafter, examples are illustrated. However, theseexamples are exemplary, and the present disclosure is not limitedthereto.

EXAMPLES Analysis Method [1] Fourier-Transform Infrared (FT-IR)Spectroscopy and Nuclear Magnetic Resonance (NMR) Analysis

A FT-IR analysis is made using Varian 670-IR with Miracle accessory anda NMR analysis is made using Bruker Advance III Ascend 500 MHz NMRspectrometer.

[2] Photoluminescence Analysis

Photoluminescence (PL) spectra of the produced nanocrystals are obtainedusing a Hitachi F-7000 spectrometer at an irradiation wavelength of 372nm.

[3] Ultraviolet (UV) Spectroscopy Analysis

UV spectroscopy analysis is performed using a Hitachi U-3310spectrometer to obtain a UV-Visible absorption spectrum.

[4] Transmission Electron Microscope (TEM) Analysis

Transmission electron microscope photographs of nanocrystals areobtained using an UT F30 Tecnai electron microscope.

[5] ICP Analysis

An inductively coupled plasma-atomic emission spectroscopy (ICP-AES)analysis is performed using Shimadzu ICPS-8100.

Synthesis is performed under an inert gas atmosphere unless particularlymentioned.

Reference Example 1: Formation of Amide Ligand

50 mL of trioctylamine is placed in reaction flask, and 9 millimoles(mmol) of oleic acid and 9 mmol of hexadecyl amine are added thereto. Aresulting mixture is heated at 280° C. for 10 minutes and then is cooledto room temperature (ca. 23° C.). The precipitated solid is separatedvia centrifugation and then is washed with hexane at least three timesand is filtered and then dried under vacuum.

An FT-IR analysis and an NMR analysis are conducted for the formedproduct and the results are shown in FIG. 5 and FIG. 6 (bottom),respectively.

An NMR analysis is also made for the mixture prior to the reaction andthe results are shown in FIG. 6 (top).

FIG. 5 and FIG. 6 confirmed that the synthesized solid includes acompound having the following structure with an amide moiety and longalkyl and alkenyl moieties:

In a NMR spectrum of FIG. 6 (bottom), a peak at 3.2 parts per million(ppm) is assigned to the one derived from the alkyl adjacent to theamide moiety.

Example 1-1: Production of ZnTeSe CORE

Selenium and tellurium are dispersed in trioctylphosphine (TOP) toobtain a 2 molar (M) Se/TOP stock solution and a 0.1 M Te/TOP stocksolution.

A 1M hexane solution of diethyl zinc is prepared.

Trioctylamine is placed in a 300 mL reaction flask and oleic acid (OA),hexadecylamine (HDA), and the amide ligand synthesized in ReferenceExample 1 are added thereto, each at a mole ratio of 1.5 moles withrespect to 1 mole of a zinc precursor (that will be described below,i.e., diethylzinc), respectively. After an atmosphere in the flask isexchanged with nitrogen, the reaction flask is heated at 280° C. for 10minutes to prepare a heat-treated ligand mixture.

After raising a temperature of the heat-treated ligand mixture to 300°C., a diethylzinc stock solution is injected into the flask and then theprepared Se/TOP stock solution and Te/TOP stock solution are rapidlyadded thereto in a Te/Se ratio of 1/25. A reaction proceeds for 40minutes at the same temperature.

After the reaction, the reaction solution is rapidly cooled to roomtemperature and ethanol is added thereto. Precipitates thus obtained aresubjected to centrifugation to recover a ZnSeTe core. The recoveredZnSeTe core particles are dispersed in toluene.

A transmission electron microscopic analysis is made for the coreparticles and the results are shown in FIG. 7. The results confirm thatthe obtained core particles have uniform particle sizes (2.5±0.3 nm) andtheir shapes are generally spherical.

With respect to the obtained core particles, a UV-vis spectroscopicanalysis and photoluminescence spectroscopic analysis are made and theresults are shown in FIG. 9, FIG. 10, and Table 1.

Example 1-2: ZnSeS Shell Formation on a ZnSeTe Core

In a 300 mL reaction flask, TOA is placed and zinc acetate and oleicacid are added thereto at a mole ratio of 1:2, then the mixture isvacuum-treated at 120° C. for 10 minutes. After the atmosphere in theflask is replaced with N₂, it is heated to 280° C. A toluene dispersionof the ZnTeSe cores prepared in Example 1-1 is injected rapidly and thenSe/TOP stock solution and S/TOP stock solution are added thereto overthree or four times (together with a Zn precursor, if desired) while themixture is heated to 320° C. and the reaction proceeds for one hour(formation of a ZnSeS layer). Finally, a S/TOP stock solution is addedthereto and the reaction goes for another 20 minutes (formation of a ZnSlayer).

After the completion of the reaction, the flask is cooled to roomtemperature and the prepared core-shell quantum dots are recovered viaprecipitation using ethanol and centrifugation. The obtained quantumdots are dispersed in toluene.

With respect to the core-shell quantum dot particles, a transmissionelectron microscopic analysis is made and the results are shown in FIG.8. The results of FIG. 8 confirm that the obtained quantum dots havemultipod shapes and an average size thereof is about 8.9 nm.

With respect to the obtained core-shell particles, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in FIG. 9, FIG. 10, and Table 1.

TABLE 1 Photoluminescence (excitation at 372 nm) Maximum peak Quantumwavelength FWHM efficiency (nm) (nm) (QE) Core particle 442 100  8%Core-shell 448 33 95% quantum dot

Results of FIG. 9, FIG. 10, and Table 1 confirm that the UV-visabsorption spectrum of the prepared core particles have an inflectionpoint, thus having a valley. In addition, the PL spectrum of the corehas a broad peak.

Results of FIG. 9, FIG. 10, and Table 1 confirm that the UV-visabsorption spectrum of the prepared core-shell particles do not reallyhave a first peak but have improved PL properties (significantlyimproved quantum efficiency and narrowed FWHM) in comparison with thoseof the core particle.

Example 2-1: Production of ZnTeSe Core (In-Situ Formation of the LigandMixture)

A ZnTeSe core is prepared in the same manner as set forth in Example 1-1except that after trioctylamine is placed in a 300 mL reaction flask,oleic acid (OA) and hexadecylamine (HDA) are added thereto, each at amole ratio of 2 mole with respect to 1 mole of a zinc precursor, anatmosphere in the flask is changed into nitrogen, and then the reactionflask is heated at 280° C. for 10 minutes to prepare a heat-treatedligand mixture.

A transmission electron microscopic analysis is made for the coreparticles and the results are shown in FIG. 11. The results confirm thatan average particle size of the obtained core particles is about 3.5 nm(standard deviation: 0.6 nm) and their shapes are generally spherical.

With respect to the obtained core particles, a UV-vis spectroscopicanalysis and photoluminescence spectroscopic analysis are made and theresults are shown in Table 2.

Example 2-2: Formation of ZnSeS Shell on the ZnTeSe Core

Except for using the core prepared in Example 2-1, a core shell quantumdot is prepared in the same manner set forth in Example 1-2.

With respect to the obtained core-shell quantum dots, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in Table 2.

With respect to the obtained core-shell quantum dots, an ICP-AESanalysis is made and the results are shown in Table 3.

Comparative Example 1-1

A ZnTeSe core is prepared in the same manner as set forth in Example 1-1except for using the ligand mixture prepared as below: trioctylamine isplaced in a 300 mL reaction flask, hexadecylamine (HDA) is added theretoat a mole ratio of 2 mole with respect to 1 mole of the zinc precursor(i.e., diethyl zinc), an atmosphere in the flask is changed intonitrogen, the reaction flask is heated at 280° C. for 10 minutes. Atemperature of the flask is raised to about 300° C., and then oleic acid(OA) is added thereto at a mole ratio of 2 mole with respect to 1 moleof the zinc precursor to obtain a heated ligand mixture including the OAand the HDA without the amide.

A transmission electron microscopic analysis is made for the coreparticles and the results are shown in FIG. 12. The results confirm thatan average particle size of the obtained core particles is about 5.1 nm(a standard deviation: 0.8 nm) and fusion between the core particlesoccurs.

With respect to the obtained core particles, a UV-vis spectroscopicanalysis and photoluminescence spectroscopic analysis are made and theresults are shown in Table 2.

Comparative Example 1-2

Except for using the core prepared in Comparative Example 1-1, a coreshell quantum dot is prepared in the same manner set forth in Example1-2.

With respect to the obtained core-shell quantum dots, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in Table 2.

TABLE 2 Photoluminescence (excitation at 372 nm) PL peak Quantumwavelength FWHM efficiency (nm) (nm) (QE, %) Example 2-1 Core particle446 106 20% Example 2-2 Core-shell QD 453 22 86% Comp. Core particle 43049 18% Example 1-1 Comp. Core-shell QD 449 26 47% Example 2-1

The results of the UV-vis spectroscopic analysis confirm that the coreparticles as prepared do not show a 1^(st) peak in the UV-vis absorptionspectrum. The results of Table 2 confirm that the core prepared inExample 2-1 has a wide FWHM and a low level of QE.

The results of the UV-vis spectroscopic analysis confirm that the coreshell QD as prepared do not show a 1^(st) peak in the UV-vis absorptionspectrum. The results of Table 2 confirm that the core-shell QDsprepared in the Example 2-2 has a narrower FWHM and a higher level of QEin comparison with the core-shell QDs prepared in the ComparativeExamples.

The results of Table 2 confirm that in Comparative Examples, the quantumdots including the core prepared without the amide ligand exhibit asignificantly lower level of the QE in comparison with that of thecore-shell QD of the Example.

TABLE 3 Mole ratio (with respect to Zn) Zn Se Te S Example 2-2 1.0000.382 0.002 0.546

Example 3: Changes in a Ratio Between the Used Carboxylic Acid Compoundand the Used Amine Compound

A core particle is prepared in the same manner set forth in Example 2-1except that the ratio between the oleic acid and the hexadecylamine andthe ratio between the selenium and the tellurium are changed as setforth in Table 4.

With respect to the obtained core particles, a UV-vis spectroscopicanalysis and photoluminescence spectroscopic analysis are made and theresults are shown in Table 4.

Except for using the core prepared as above, a core shell quantum dot isprepared in the same manner set forth in Example 1-2.

With respect to the obtained core-shell quantum dots, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in Table 4.

TABLE 4 Core particle Core-shell QD (PL excitation at 372 nm) (PLexcitation at 372 nm) PL maximum PL maximum OA:HDA Te/Se peak wavelengthFWHM QE peak wavelength FWHM QE (mole ratio) (mole ratio) (nm) (nm) (%)(nm) (nm) (%) 2:1 1/30 435 58 36 448 33 64 3:2 1/36 431 52 39 445 28 722:2 1/36 446 106 20 447 36 89 3:3 1/36 433 108 16 447 33 84 2:3 1/36 45594 11 446 32 82 1:2 1/30 477 144 2 454 42 73 1:4 1/36 592 74 1 457 52 510:5 1/36 Zn metal formation (impossible — — — to obtain a core particle)

The results of Table 4 confirm that when the ligand mixture does notinclude a relatively excess amount of the amide ligand at the time offorming the core, the core-shell quantum dot as prepared exhibitrelatively poor luminous properties (e.g., a wider FWHM and a lower QE).

Example 4

A core particle is prepared in the same manner as set forth in Example2-1 except that oleylamine is used instead of hexadecyl amine and 1.5mole of the oleic acid and 1 mole of the oleylamine are used withrespect to 1 mole of the zinc precursor, respectively.

A transmission electron microscopic analysis is made for the coreparticles and the results are shown in FIG. 13. The results confirm thatthe obtained core particles have relatively uniform particle sizes andtheir shapes are generally spherical. With respect to the obtained coreparticles, a UV-vis spectroscopic analysis and photoluminescencespectroscopic analysis are made and the results are shown in Table 5.

Except for using the core prepared as above, a core shell quantum dot isprepared in the same manner set forth in Example 1-2.

With respect to the obtained core-shell quantum dots, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in Table 5.

With respect to the core-shell quantum dot particles, a transmissionelectron microscopic analysis is made and the results are shown in FIG.14. The results of FIG. 14 confirm that the obtained quantum dots havemultipod shapes.

With respect to the obtained core-shell particles, a UV-visspectroscopic analysis and photoluminescence spectroscopic analysis aremade and the results are shown in Table 5.

TABLE 5 Photoluminescence (excitation at 372 nm) Maximum PL peak Quantumwavelength FWHM efficiency (nm) (nm) (QE) Core particle 443 77 12%Core-shell QD 445 31 83%

While this disclosure has been described in connection with what ispresently considered to be practical example embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A quantum dot comprising: a core comprising afirst semiconductor nanocrystal material comprising zinc, tellurium, andselenium; and a shell disposed on at least a portion of the core andcomprising a second semiconductor nanocrystal material different fromthe first semiconductor nanocrystal material, wherein the quantum dotdoes not comprise cadmium, wherein a maximum luminescent emission peakof the quantum dot is in a wavelength range from about 440 nanometers toabout 560 nanometers, wherein the quantum dot has a quantum efficiencyof greater than or equal to about 60%, wherein the first semiconductornanocrystal material comprises ZnTe_(x)Se_(1−x), wherein x is greaterthan 0 and less than or equal to about 0.2, and wherein the secondsemiconductor nanocrystal material comprises Zn and at least one of Seand S.
 2. The quantum dot of claim 1, wherein the x is less than orequal to about 0.09.
 3. The quantum dot of claim 1, wherein the secondsemiconductor nanocrystal material comprises zinc and selenium.
 4. Thequantum dot of claim 1, wherein the second semiconductor nanocrystalmaterial comprises zinc and sulfur.
 5. The quantum dot of claim 1,wherein the second semiconductor nanocrystal material comprises zinc,selenium, and sulfur.
 6. The quantum dot of claim 1, wherein the shellhas a first layer comprising a third semiconductor nanocrystal and asecond layer disposed on the first layer and comprising a fourthsemiconductor nanocrystal that is different from the third semiconductornanocrystal.
 7. The quantum dot of claim 6, wherein the thirdsemiconductor nanocrystal comprises zinc, selenium, and optionallysulfur, and wherein the fourth semiconductor nanocrystal comprises zincand sulfur.
 8. The quantum dot of claim 1, wherein a plurality of thequantum dots are water-insoluble.
 9. The quantum dot of claim 1, whereinin the quantum dot, a mole ratio of a sum of S and Se with respect to Znis greater than or equal to about 0.3.
 10. The quantum dot of claim 1,wherein in the quantum dot, a mole ratio of sulfur with respect to zincis greater than or equal to about 0.1.
 11. The quantum dot of claim 1,wherein the quantum dot further comprises an organic ligand and theorganic ligand comprises RCOOH, RNH₂, R₂NH, R₃N, RSH, RH₂PO, R₂HPO,R₃PO, RH₂P, R₂HP, R₃P, ROH, RCOOR, RPO(OH)₂, RHPOOH, RHPOOH, or acombination thereof, wherein R is the same or different andindependently is a C1 to C40 aliphatic hydrocarbon group, a C6 to C40aromatic hydrocarbon group, or a combination thereof.
 12. The quantumdot of claim 1, wherein the maximum luminescent emission peak of thequantum dot has a full width at half maximum of less than or equal toabout 50 nanometers.
 13. The quantum dot of claim 1, wherein the quantumdot has a multi-pod shape.
 14. The quantum dot of claim 1, wherein thequantum dot has a quantum efficiency of greater than or equal to about70%.
 15. An electronic device comprising the quantum dot of claim
 1. 16.An electroluminescent device comprising an anode and a cathode facingeach other and a quantum dot emission layer comprising a plurality ofquantum dots, wherein the plurality of quantum dots comprises thequantum dot of claim
 1. 17. The electroluminescent device of claim 16,further comprising a charge auxiliary layer between the anode and thecathode.
 18. An electronic device comprising a quantum dot, wherein thequantum dot comprises zinc, tellurium, and selenium; wherein the quantumdot does not comprise cadmium, wherein in the quantum dot, a mole ratioof tellurium with respect to selenium is greater than or equal to about0.001 and less than or equal to about 0.1, wherein a maximum luminescentemission peak of the quantum dot is in a wavelength range from about 440nanometers to about 470 nanometers, and wherein the quantum dot has aquantum efficiency of greater than or equal to about 60%.
 19. Theelectronic device of claim 18, wherein in the quantum dot, the moleratio of the tellurium with respect to the selenium is less than orequal to about 0.08.
 20. The electronic device of claim 18, wherein inthe quantum dot, a mole ratio of tellurium with respect to zinc isgreater than or equal to about 0.0001 and less than or equal to about0.03.
 21. The electronic device of claim 18, wherein the quantum dotcomprises sulfur and in the quantum dot, a mole ratio of sulfur withrespect to zinc is greater than or equal to about 0.1.
 22. Theelectronic device of claim 18, wherein the quantum dot has a multipodshape having at least two branches and a valley between the branches.23. The electronic device of claim 18, further comprising an anode and acathode facing each other; and a layer disposed between the anode andthe cathode, wherein the quantum dot is included in the layer.